This invention relates to high intensity arc discharge lamps and particularly to metal halide-mercury lamps operated in a vertical position.
One of the serious problems that occurs in halide-mercury high intensity discharge lamps is the separation of color which results when the arc of the lamp is positioned in a vertical or nearly vertical position. Typically, in the higher wattage, physically longer lamps containing a sodium halide as one of the ingredients, the orange color of the sodium radiation appears predominately at the bottom of the discharge arc, leaving the radiation of other ingredients, including mercury, which is generally blue or blue-green, in the upper portion of the discharge arc. These lamps are typically operated at a positive column arc gradient of between approximately 25 and 35 v/cm. The color separation results in uneven distribution of color in the area being illuminated and in addition is accompanied by substantial loss of luminous efficacy.